Compound electrostatic lens system

ABSTRACT

A cylindrical electrostatic electrode system for use as an electron lens. Several cylindrical sections, while insulated from each other, are provided with complimentary end serrations and abutted together. The serrations are rotationally symmetrical with repetition factors of eight or higher. The electrode segments are provided with different potentials, whereby axial potential distribution can be closely controlled with no resulting low-order angular dependent lens aberrations.

United States Patent [191 Hutter et al.

[ June 17, 1975 COMPOUND ELECTROSTATIC LENS SYSTEM [75) Inventors:Rudolf G. E. Butter, New York,

N.Y.; Herman O. Dressel, Lynnfield, Mass.

[73] Assignee: GTE Laboratories Incorporated,

Waltham, Mass.

22 Filed: May 28,1974

211 Appl.No.:473,539

52 use: ..313/460;3l5/ISX 5| Int. Cl HOlj 29/02; HOlj 29/48 58 FieldofSearch ..313/44|.450, 449, 44s,

[56] References Cited UNITED STATES PATENTS 3,73l.l36 5/l973 Roussin313/434 X Primary ExaminerRobert Segal Attorney, Agent, or Firmlrving M.Kriegsman; Leslie J. Hart [57] ABSTRACT 5 Claims, 6 Drawing FiguresCATllOM COMPOUND ELECTROSTATIC LENS SYSTEM BACKGROUND OF THE INVENTIONl. FIELD ,OF THE. INVENTION This invention relates to eiectrostaticelectron lenses, and especially to multi-electrode cylindrical lenses ofthe type used in cathode-ray tubes.

2. DESCRIPTION OF THE PRIOR ART US. Pat. No. 3,678,320 to Bartendescribes an electrode system for cathode-ray tubes in which twoadjacent cylindrical grids are abutted at a preferably sinusoidal set ofcrenels. The number of sinusoidal cycles around the circumference of thegrids is normally three, which is both low in number and nonsymmetrical,resulting in low order angular dependent lens aberrations.

US. Pat. No. 2,080,449 to von Ardenne discloses an electrode system foruse in a cathode-ray tube in which one electrode is used to focus theelectron beam and another electrode, which is compound of cylindricalsections, is used to accelerate the focused beam.

U.S. Pat. No. 2,312,723 to Llewellyn discloses an electrode system inwhich two adjacent cylinders are abutted at a cyclic crenel to producean accelerating electrode. Llewellyn changes the cylinders into conesfor use in focusing.

SUMMARY OF THE INVENTION By the use of at least three cylinderssubstantially abutted but insulated at serrated or crenellated joints,and where the potential distribution is rotationally symmetrical aboutthe cylinder axis everywhere the electron beam traverses the lens, anEinzel lens can be constructed. If the angular dependent terms aremultiplied by radius factors of eight or higher, as by constructingserrations with octupolar (or higher order) symmetry, then evenfifth-order lens aberrations are not affected bynon-rotationally-symmetrical components of the potential distribution.This analysis is closely confirmed by experiment, so that the axialpotential distribution may safely be used to calculate paraxial andthird order lens properties. Furthermore, if one can assume that thepotential variation across the insulated gap between cylinders islinear, then the potential distribution is essentially the same as thatfor truly rotationally symmetrical structures.

The shape of the serrations can be chosen to alter the potentialvariation along the cylinder while entrance and exit poteptials andlength and radius of the lens remain constant.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall view of acompound electrode lens system according to the invention.

FIG. 2 is a cross-sectional view of a portion of the electrode to showone mode of construction.

FIGS. 3, 4 and 5 illustrate developed or unrolled forms of threeoctupolar electrodes of three cylindrical electrode sections each.

FIG. 6 illustrates a developed l2-pole electrode of three cylindricalelectrode sections.

FIG. 7 illustrates a developed octupolar electrode of four cylindricalelectrode sections.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. I is an overall diagram ofa compound electrostatic electrode system according to the presentinvention. An electron beam e is supplied by a cathode 2 and directedthrough a compound cylindrical electrode to a target which is notillustrated. The electrode illustrated in FIG. 1 comprises first, secondand third cylindrical electrode sections 6, 8 and 10. The first electrode section 6 is even ended at one end 12 and terminates in serrationsof a first pattern at its other end I4. The second electrode section 8has one of its ends 16 substantially adjacent to but insulated from theend 14 of the first section 6. End 16 of section 8 terminates inserrations which complement or fill in the serrations of the firstpattern in end 14. The other end 18 of electrode section 8 terminates inserrations ofa second pattern, which may be the same as or differentfrom the first pattern. The third section I0 has one end 20substantially adjacent to but insulated from the end I8 of the secondsection 8. The end 20 of the third section terminates in serrationswhich complement or fill in the serrations of the second pattern in end18. The other end 22 of electrode section is even ended.

A means is provided for applying chosen potentials V V and V to each ofthe three sections. In a preferred embodiment in which the electrostaticlens system is used as an Einzel lens, potentials V, and V are equal,while potential V is different.

The first and second patterns are cyclic patterns which repeat aroundthe circumference of the cylindrical sections. The patterns preferablyrepeat at least eight times around the circumference, so that angulardependent terms for potential distribution within the cylindricalelectrodes are multiplied by radius factors (measured from the cylinderaxis) of the order eight or higher, whereby even fifth-order lensaberrations are not affected by non-rotationally symmetrical componentsof the potential distribution.

The pattern must be circumferentially periodic and must be of higherorder than octupolar symmetry. For such symmetry, a diameter lineconstructed at any point on the cylindrical axis of the electrode androtated to any rotational position will find points of equal potentialat its opposite ends.

FIG. 2 illustrates a preferred method of constructing such a compoundelectrode. A non-conductive substrate 26 (shown in cross section) formsthe outer wall of electrode 4 and is plated on its inside surface withpatterned metal conductors 28 separated by empty insulation gaps 30.

FIGS. 3, 4 and 5 illustrate electrode systems with octupolar symmetry.These figures represent developed or unrolled versions of thecylindrical electrode system as in FIG. 1. The embodiment of FIG. 3 usesfirst and second patterns of serrations, both of which are in a sawtoothform. As illustrated, the cylindrical sections 6, 8 and 10 are separatedby a narrow non-conductive ribbon such that each cylindrical section issubstantially adjacent to but insulated from the adjacent cylindricalsection. The embodiments of FIGS. 4 and 5 use curved cyclical patternsof serrations.

FIG. 6 illustrates a symmetrical pattern of higher order than eight.Specifically, this cylical pattern repeats twelve times around thecircumference.

FIG. 7 illustrates an electrode system in which the middle electrodesection 8 is further broken down into two subsections 8a and 8b whichare substantially adjacent to but insulated from each other. Thesesubsections may have different voltages applied thereto. The use ofsubsections allows the use of multiple potential steps in sequence,thereby distributing the potential change at the boundary over manyinsulated regions, reducing the breakdown problem between adjacentelectrodes.

What is claimed is:

l. A compound electrostatic electrode lens system for combined focusingand acceleration of an electron beam comprising:

A. first, second and third cylindrical electrode sections,

By the first section being even ended at one end and terminating inserrations of a first pattern at its other end,

C, the second section having one end substantially adjacent to butinsulated from the other end of the first section, the one end of thesecond section terminating in serrations which fill in the serrations ofa first pattern of the first section, the other end of the secondsection terminating in serrations of a second pattern,

D. the third section having one end substantially adjacent to butinsulated from the other end of the second section, the one end of thethird section terminating in serrations which fill in the serrations ofa second pattern of the second section, the other end of the thirdsection being even ended, and

E. means for applying chosen potentials to each of the three sections,

wherein both the first pattern and the second pattern are cyclicpatterns which repeat at least eight times around the circumference ofthe cylindrical sections and which are diametrically symmetrical withrespect to the axis of the cylindrical sections at all points on theaxis and all rotational positions of the diameter.

2. A system according to claim 1 for use as an Einzel lens wherein themeans for applying chosen potentials comprises means for applying afirst potential to the first and third sections and for applying asecond potential to the second section.

3. A system according to claim 1 wherein the cyclic patterns repeateight times around said circumference.

4. A system according to claim 1 wherein at least one of said patternsis a sawtooth pattern.

5. A system according to claim 1, wherein the second section is dividedinto a plurality of cylindrical subsections arranged in axial sequencealong the electrode system, the ends of two end subsections forming theend of the second section, subsections being substantially adjacent tobut insulated from sequential subsections with further symmetricalpatterns of serrations therebetween.

1. A compound electrostatic electrode lens system for combined focusingand acceleration of an electron beam comprising: A. first, second andthird cylindrical electrode sections, GB. the first section being evenended at one end and terminating in serrations of a first pattern at itsother end, C. the second section having one end substantially adjacentto but insulated from the other end of the first section, the one end ofthe second section terminating in serrations which fill in theserrations of a first pattern of the first section, the other end of thesecond section terminating in serrations of a second pattern, D. thethird section having one end substantially adjacent to but insulatedfrom the other end of the second section, the one end of the thirdsection terminating in serrations which fill in the serrations of asecond pattern of the second section, the other end of the third sectionbeing even ended, and E. means for applying chosen potentials to each ofthe three sections, wherein both the first pattern and the secondpattern are cyclic patterns which repeat at least eight times around thecircumference of the cylindrical sections and which are diametricallysymmetrical with respect to the axis of the cylindrical sections at allpoints on the axis and all rotational positions of the diameter.
 2. Asystem according to claim 1 for use as an Einzel lens wherein the meansfor applying chosen potentials comprises means for applying a firstpotential to the first and third sections and for applying a secondpotential to the second section.
 3. A system according to claim 1wherein the cyclic patterns repeat eight times around saidcircumference.
 4. A system according to claim 1 wherein at least one ofsaid patterns is a sawtooth pattern.
 5. A system according to claim 1,wherein the second section is divided into a plurality of cylindricalsubsections arranged in axial sequence along the electrode system, theends of two end subsections forming the end of the second section,subsections being substantially adjacent to but insulated fromsequential subsections with further symmetrical patterns of serrationstherebetween.